The ubiquitous nature of the Horizontal Branch second U-jump: A link with the Blue Hook scenario?

Details The ubiquitous nature of the Horizontal Branch second U-jump: A link with the Blue Hook scenario? The ubiquitous nature of the Horizontal Branch second U-jump: A link with the Blue Hook scenario?

2004-02-25

arxiv.org/abs/astro-ph/0402594v1

Astron.Astrophys. 420 (2004) 605-617

Astronomy and Astrophysics

Astrophysics

15 pages, 8 figures. Higher resolution version available via ftp at ftp://ftp.pd.astro.it/pub/momany/momany.tar A&A accepted

Scientific paper

10.1051/0004-6361:20035699

In a previous paper we reported on a discontinuity in the extreme horizontal branch (EHB) of the Galactic globular cluster NGC6752, which we called the second U-jump. This feature was attributed to a combination of post zero-age horizontal branch evolution and diffusion effects. In this follow-up study we analyze other EHB clusters and show that the second U-jump is a common feature among EHB clusters reaching T_{eff}\ge 23,000K, and that its onset in different clusters converges around T_{eff}\sim 21,000\pm3,000K. We also present near-ultraviolet diagrams of \omega Cen and NGC2808, the only two objects with spectroscopically confirmed ``blue hook'' stars (T_{eff}\ge 35,000K). We confirm predictions of a photometric discontinuity separating late from early-helium flashers. Moreover, we present empirical evidence that the second U-jump population might be mainly composed by early-helium flashers. Lastly, we revisit the discussion on the ubiquitous nature of the gaps and jumps so far identified in the blue HB tails, suggesting a possible discrete nature of the distribution in temperature of the HB stars.

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